Automated subcool control

ABSTRACT

The present disclosure relates to a method and system for automated subcool control, wherein the controller is a traditional proportional integral controller based on gap control low select logic and the output controls pump speed for the artificial lift pump.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to 61/946,511, filed Feb. 28, 2014, which is incorporated by reference herein in its entirety for all purposes.

FEDERALLY SPONSORED RESEARCH STATEMENT

Not applicable.

FIELD OF THE DISCLOSURE

The disclosure relates to a method and system for controlling the subcool in steam-assisted oil recovery techniques, such as SAGD.

BACKGROUND OF THE DISCLOSURE

Oil sands are a type of unconventional petroleum deposit. The sands contain naturally occurring mixtures of sand, clay, water, and a dense and extremely viscous form of petroleum technically referred to as “bitumen,” but may also be called heavy oil or tar. Many countries in the world have large deposits of oil sands, including the United States, Russia, and various countries in the Middle East. However, the world's largest deposits occur in Canada and Venezuela.

The crude bitumen contained in the Canadian oil sands is described as existing in the semi-solid or solid phase in natural deposits. Bitumen is so heavy and viscous (thick) that it will not flow unless heated or diluted with lighter hydrocarbons. At room temperature, bitumen is like cold molasses and when cold it is solid. Due to its high viscosity, these heavy oils are hard to mobilize, and they generally must be made to flow in order to produce and transport them.

Steam assisted gravity drainage (SAGD) is a commercial recovery process used for recovering heavy oil and bitumen that possess low to no mobility under native reservoir conditions. In SAGD steam is circulated within horizontal injection and production wells that are spaced vertically 5 meters apart and placed near the base of the reservoir. Once fluid communication is established between the wells, the top well is operated as a dedicated injector well, and the bottom well as a producer well. With time, the steam melts the bitumen directly above the injector well and the resulting fluid is produced via gravity drainage to the base of the reservoir. Once steam reaches the top of the reservoir, the steam chamber spreads horizontally within the reservoir, creating a steam chamber. As steam continues to be injected, the latent heat of vaporization of water drives the ability to melt and subsequently drain fluids for production. In the SAGD process, the produced fluid consists of an oil and water emulsion that can contain as much as 70% (w/w) water.

The rate at which fluid is produced by the reservoir is driven by both gravity drainage and the subcool. Subcool is the difference between the saturation temperature (boiling point) of water at the producer pressure and the actual temperature at the same place where the pressure is measured. A normal subcool is illustrated in FIG. 1B and 1C. In FIG. 1C, steam is injected through the injection well 101 and forms a steam chamber 105. The bitumen 107 thus mobilized by the steam chamber is gravity drain through the production well 103, where certain amount of liquid 109, including condensed water, accumulates above the production well 103. If the subcool gets too low, the steam can reach all the way to the producer, thus resulting in steam breakthrough (see FIG. 1A).

The biggest risk to damaging SAGD wells is flashing steam across the liner, which occurs when the fluid that is coming into the well drops to its saturation pressure for the temperature it is at as it passes through the liner. At this point, the fluid undergoes a phase change from liquid to vapor (steam), thus velocity increases substantially and can wash out liners, compromising ability to control sand. Such incidents damage equipment and result in downtime, thus costing millions on each occurrence.

Steam breakthrough is avoided by using “steam trap” control, wherein a liquid pool is maintained in the region surrounding the production well by increasing the subcool. This liquid pool contains mobilized bitumen and steam condensate and is similar in concept to steam traps used in steam heaters and prevents steam flowing directly from the injector to the producer.

A high temperature difference (high subcool) allows a reduction of steam injection rates and prevents steam breakthrough, but it also results in slightly reduced production due to a corresponding higher viscosity and lower mobility of bitumen caused by the lower temperature. Another drawback of very high subcool is the possibility of steam pressure eventually not being enough to sustain steam chamber development above the injector, sometimes resulting in collapsed steam chambers where condensed steam floods the injector and precludes further development of the chamber. Further, when the level of fluids above the injector becomes higher, the available height for gravity drainage at the edges of the chamber is correspondingly reduced so the production rate will further suffer.

In field operations, the liquid level of the subcool cannot be measured directly. However, continued existence of the liquid pool is monitored by examining the temperature difference between the injected steam and produced fluids. This temperature difference is called the interwell subcool or the reservoir subcool. FIG. 1C thus illustrates the problem, that of driving this temperature differential towards an optimal level. A rule-of-thumb estimation of 10° C./m of liquid level has established its popularity in the industry, although it is not always correct and furthermore, it is difficult to achieve on an ongoing dynamic basis.

Petroleum engineers have considered the problem of subcool control. For example, SPE122014: SAGD Subcool Control with Smart Injection Wells (2012) by Gotawala describes the use or Proportional-Integral-Derivative (PID) feedback control to control inflow valve settings to promote subcool to a target value. Specifically, the SAGD injector is divided into six intervals each with its own steam injection pressure. Interval control valves (ICVs) were used to control the injection or production of fluids at specified sections of the well. The interwell subcool was calculated and the PID feedback control algorithm used to direct the subcool to a target value by changing the steam injection pressure in each well interval. The equation used was:

$P_{i}^{new} = {P_{i}^{old} + {K_{p}ɛ_{i}} + {K_{D}\frac{ɛ_{i}}{t}} + {K_{I}{\int_{t = 0}^{I_{new}}{{ɛ_{i}(\tau)}\ {\tau}}}}}$

where P is pressure, t is time, τ is the integration variable and ε is the error between actual subcool and target subcool. P_(i) is the steam injection pressure of interval i and K_(p), K_(D), and K_(I) are the proportional, derivative, and integral control gains, respectively.

The algorithm was programmed as in FIG. 4.

This method was simulated using CMG STARS™ for a two-year period and showed that the cSOR of the controlled operation was lower, especially early in the operation, than that without control. Steam chamber development was more uniform, although there were still variations in chamber height. Furthermore, the method is complex, and requires the use of ICVs, which are not always available, and the use of the derivative makes the system overly sensitive to noise. Additionally, the method uses different control variables (injection control) in the injection well, not the producer.

WO2013025420 describes another method using PID control logic. However, this method is also based on steam injection control, and utilizes the derivative and thus is sensitive to measurement noise. As above, the method uses different variables in the injection wells.

Thus, what is needed in the art is a better method of controlling the subcool, and thus optimizing oil production and steam use. Such a method would ideally be simpler, less sensitive to noise in measurements and be compatible with common well completion technology.

SUMMARY OF THE DISCLOSURE

The present disclosure provides a novel method and system for controlling the subcool for optimal oil production.

Generally speaking, the method uses commonly available PI controllers (or PID controllers with D set to zero) to optimize the motor speed on the Electrical Submersible Pumps (ESP), thereby changing the rate at which liquid (hydrocarbons and water) is produced, thereby affecting the subcool and fluid levels.

The present disclosure includes one or more of the embodiments listed herein, in any combinations of one or more thereof:

-   -   A method of subcool control in steam assisted gravity drive oil         production, wherein a subcool is desirably kept at a target         subcool using a PI controller having an output that controls         pump motor speed using a PI and gap control algorithm based on         subcool temperature, and secondary PI controller(s) intervene in         a low select algorithm arrangement when ii) a high alarm set         point for motor current is nearly reached or iii) a low alarm         set point for submergence pressure is nearly reached.     -   An improved method of subcool control in steam assisted gravity         drive oil production, wherein steam is injected into a top         horizontal well to mobilize heavy oil which gravity drains to a         bottom production well and is then pumped to the surface using a         pump and where a subcool is desirably kept at a target subcool,         the improvement comprising automatically keeping a subcool at         target subcool using a PI controller having an output that         controls pump motor speed using a low select algorithm based         primarily on gap control of subcool temperature.     -   A method of automated subcool control in a steam-assisted         gravity drive oil well, comprising:

providing a producer well having one or more temperature sensors therein for measuring a temperature of a production fluid (Tb) and one or more pressure sensors for measuring pressure (Pb) at bottomhole conditions, and one or more pressure sensors for measuring pressure at a casing head (Pc);

providing a pump motor fluidly connected to said producer well for pumping a production fluid to the surface;

calculating a submergence pressure Sp=Pb−Pc;

calculating a steam saturation temperature (Ts) at Pb and Tb using e.g., an equation that approximates steam tables;

providing a primary proportional integral (PI) controller for controlling subcool temperature (TIC) based on a gap control algorithm;

providing a secondary proportional integral (PI) controller for controlling a current of said motor (IIC) when said pump motor's current approaches a high alarm set point;

providing a secondary proportional integral (PI) controller for controlling a submergence pressure (PDIC) when said submergence pressure approaches a low alarm set point;

wherein each PI controller feeds a low select algorithm to select the control signal that adjusts said speed of said motor so as to approach a target subcool temperature (TΔ=Ts−Tb), maintain acceptable motor current, and/or acceptable liquid column or (submergence pressure) level.

-   -   A system for automated subcool control of a steam assisted oil         recovery; said system including a gap control PI controller that         adjusts a pump motor's speed to maintain a target subcool, and         includes a PI controller for low select intervention when said         pump motor's speed approaches a high alarm value and includes a         PI controller for a low select intervention when a submergence         pressure approaches a low alarm value.     -   A method or system as herein described including a producer well         having one or more temperature sensors therein for measuring a         temperature of a production fluid (Tb) and one or more pressure         sensors at bottomhole conditions (Pb) and one or more pressure         sensors at a casing head (Pc).     -   A method or system as herein described wherein said target         subcool (TΔ) temperature is between 5-15° C./m with a gap         allowance of 1-5° C., or 7-12° C./m with a gap allowance of         ±1-3° C.     -   A method or system as herein described wherein a secondary PI         control system intervenes with a low select algorithm when ii) a         high alarm set point for motor current is reached or iii) a low         alarm set point for submergence pressure is reached.     -   A method or system as herein described including an override         function whereby said pump motor's speed cannot be increased         when a temperature of said pump motor reaches a high alarm         point.

As used herein “providing” is intended to include use of existing equipment, as well as the provision of new equipment. Thus, providing a producing well, for example, can include using an existing well.

As used herein, “subcool temperature” is defined as the temperature difference between the produced fluid's steam saturation temperature corresponding to the pressure measured at the pump intake and the highest measured temperature along the producer well lateral. It is usually ascertained by temperature measurement devices installed and equally spaced in the producer well's horizontal section.

As used herein “motor current” is the electrical current provided to the motor that provides artificial lift to produce heavy oils in many SAGD and steam-flooding applications.

As used herein, “submergence pressure” is defined as the liquid column in the casing annular space above the pump. For simplicity herein it is calculated from the pressure differential between the Pump Intake Pressure and the Casing Head Pressure. This represents the theoretical liquid column above the pump intake in the casing annulus. For a precise value, a more complex calculation including water cut and a foamy area would be needed, however the composition of the liquid column in the SAGD wells is often not known. For this reason, the calculation used herein uses the difference between the pump intake pressure (measured) and the casing head pressure (measured). This value has been set to a minimum to ensure the pump will not see gas at the intake. In the future, a more precise calculation or measure can be used to increase the accuracy.

By “low select algorithm” what is meant is that the algorithm chooses the least increase in output or the largest decrease in output. For example, from two current signals of 7 mA and 12 mA, a low select algorithm will select 7 mA as the output signal.

“Gap control” or a “deadband” is used in this algorithm instead of a simple, single control set point. A “deadband (sometimes called a neutral zone) is an interval of a signal domain or band where no action occurs (the system is dormant or unchanging). Deadband is used in voltage regulators and other controllers to prevent oscillation or repeated activation-deactivation cycles (called ‘hunting’ in proportional control systems). “Gap control” as used herein is similar, but allows small changes within the gap, and larger changes outside the gap. For example, a gap is set for temperatures ranging from 60° F. to 70° F. with the target set at 65° F., and therefore the controller action remains unchanged when the temperature is within the gap.

The use of the word “a” or “an” when used in conjunction with the term “comprising” in the claims or the specification means one or more than one, unless the context dictates otherwise.

The term “about” means the stated value plus or minus the margin of error of measurement or plus or minus 10% if no method of measurement is indicated.

The use of the term “or” in the claims is used to mean “and/or” unless explicitly indicated to refer to alternatives only or if the alternatives are mutually exclusive.

The terms “comprise,” “have,” and “include” (and their variants) are open-ended linking verbs and allow the addition of other elements when used in a claim. The phrase “consisting of” excludes other elements. The term “consisting essentially of” occupies a middle ground, allowing the inclusion of nonmaterial elements, such as buffers, salts, proppants, and the like, that do not materially change the novel features or combination of the disclosed methods.

The following abbreviations are used herein:

BOPD barrels per day (aka BPD, bbl/d, bpd, bd, or b/d) cSOR Cumulative steam to oil ratio CSS Cyclic steam stimulation, aka huff-an-puff CWE Cold water equivalent ES-SAGD Expanding solvent SAGD ICV Inflow control valve IIC Electrical Current Indicating Controller (the Motor Current Control). JAGD J-well SAGD PDIC Pressure Differential Indicating Controller (the Submergence Control). PI controller proportional-integral controller (can be a PID controller with D set to zero) PID controller proportional-integral-derivative controller SAGD Steam assisted gravity drainage TIC Temperature Indicating Controller (the Subcool Temperature Control). VFD Variable-frequency drive SP Set point PV Process variable

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A-C shows cross sections of a SAGD well pair. FIG. 1A shows a cross section of a typical SAGD well pair and steam chamber. In this figure, there is a low subcool, and the steam chamber is approaching the lower producer well, potentially resulting in steam breakthrough to the producer and resulting well damage. In FIG. 1B, the subcool is higher, thus there is more fluid over the producer (see dotted line) protecting the producer from steam breakthough, but also slowing production down. FIG. 1C provides a schematic of the problem of driving the subcool AT to an optimal level.

FIG. 2A-C shows a simple schematic of P, PI and PID controllers.

FIG. 3 shows a schematic of the PI implementing logic algorithm. PID is a

Proportional-Integral-Derivative (PID) feedback controller with D=0 (aka a PI controller); PDIC=Pressure Differential Indicating Controller (the Submergence Controller); TIC=Temperature Indicating Controller (the Subcool Temperature Control); IIC=Electrical Current (“I) Indicating Controller (the Motor Current Control).

FIG. 4 shows a Proportional-Integral-Derivative (PID) feedback control algorithm to control inflow valve settings to promote subcool to a target value.

DETAILED DESCRIPTION

Wellbore and reservoir dynamics are quite unpredictable. If, on top of that, one considers the continuous changes the SAGD operations have, the proper optimization of the wellbore subcool and the production to adjust to those plays a key role in well efficiency and economics. Having a dedicated set of eyes (operator) monitoring well operating parameters is impractical and the response to trends is proven to not happen until the alarm values are reached. With this operating mode, the adjustments to problematic trends tend to be very reactive and sudden, adding more instability to the system.

The implementation of an automatic control based on subcool helps to relieve the operator from the surveillance portion of his workload and allows a proactive response to trends, maximizing production and minimizing well damage risks.

With the methods, devices and systems described herein, production losses associated with non-optimized subcool in SAGD wells can be minimized. Manual subcool optimization, in contrast, creates losses in production in the range of 10 to 100 bopd per well. The method can also minimize the risk of liner damage due to too low subcool and steam breakthrough to the liner. This type of damage creates up to 2 MM$ in asset damage and 10 MM$ in business interruption per occurrence.

The method or system uses three industrial standard PI (proportional integral) controllers. These types of controllers are used because of industry/personnel familiarity (i.e. minimal training), ease of configuration, and ease of troubleshooting. Although the individual controller algorithms are common, the control variables used in the controllers and the way in which the controllers are arranged and selected is unique, based on primary control using gap based control of subcool temperature with low select interventions in the case of i) a high alarm set point being reached or nearly reached for motor speed, and ii) a low alarm set point being reached or nearly reached for submergence pressure.

A PID controller calculation (see FIG. 2C) involves three separate parameters: the Proportional, the Integral and the Derivative. The proportional value determines the reaction to the current error; the integral value determines the reaction based on the sum of recent errors and the derivative value determines the reaction based on the rate at which the error has been changing. The weighted sum of these three actions is used to adjust the process via a control element such as the position of a control valve or the power supply of a heating element.

By tuning these three values in the PID algorithm, the controller can provide control action designed for specific process requirements. The response of the controller can be described in terms of the responsiveness of the controller to an error, the degree to which the controller overshoots the set point and the degree of system oscillation. It should be noted that the use of the PID algorithm for control does not guarantee optimal control of the system or system stability.

In the absence of knowledge of the underlying process, a PID controller has historically been considered to be the best controller. By tuning the three parameters in the PID controller algorithm, the controller can provide control action designed for specific process requirements. However, most PID systems are poorly tuned, and as discussed above, the derivative is known to be sensitive to noise in measurements.

The P-Only controller, in contrast, is easy to tune and maintain (see FIG. 2A), but whenever the set point or a major disturbance moves the process from the design level of operation, a sustained error between the process variable (PV) and set point (SP), called offset, results. Thus, its implementation can be limiting and this system provides an insufficient degree of control.

The Proportional-Integral (PI) controller (see FIG. 2B) computes and transmits a controller output (CO) signal every sample time, T, to the final control element (e.g., valve, variable speed pump, etc.). The computed CO from the PI algorithm is influenced by the controller tuning parameters and the controller error, e(t). PI controllers thus have two tuning parameters to adjust. While this makes them more challenging to tune than a P-Only controller, they are not as complex as the three-parameter PID controller, discussed by Gotawala (2012) and shown in FIG. 2C. Integral action enables PI controllers to eliminate offset, a major weakness of a P-only controller. Thus, PI controllers provide a balance of complexity and capability that makes them by far the most widely used algorithm in process control applications.

The controller output in a PI controller is given by:

K_(P)Δ+K_(I)∫Δdt

where Δ is the error or deviation of actual measured value (PV) from the setpoint (SP).

Δ=SP−PV

A PI controller can be modeled easily in software such as Simulink or Xcos using a “flow chart” box involving Laplace operators:

$C = \frac{G\left( {1 + {\tau \; s}} \right)}{\tau \; s}$

where

G=K_(P)=proportional gain

G/σ=K_(I)=integral gain

Setting a value for G is often a trade off between decreasing overshoot and increasing settling time.

The lack of derivative action makes the system steadier in the case of noisy data. This is because derivative action is more sensitive to higher-frequency terms in the inputs. Without derivative action, a PI-controlled system is less responsive to real (non-noise) and relatively fast changes in state and so the system will be slower to reach setpoint and slower to respond to perturbations than a well-tuned PID system may be. This is beneficial in the SAGD context because there are continuous fluctuations on the input parameters that are fed into the control algorithm, especially the pump submergence, the temperature and the motor current. If a derivative action were included in the SAGD control logic, the ESP system would inflict continuous and frequent motor speed changes, which have a negative impact in the system runlife.

The algorithm used herein is a low select between the output of three different PI controllers (e.g., whichever controller provides the smallest positive or largest negative change to the motor speed is dominant at that time point). The three PI controllers provide subcool temperature control, motor current control and submergence pressure control (i.e. vertical liquid column). The main or primary controller is the subcool controller, which also uses gap control with the PI algorithm. The two secondary controllers use only a PI algorithm.

The inputs for the PI controllers are the bottomhole pressure (Pb), bottomhole temperature (Tb), pressure at the casing head (Pc). The submergence pressure (Sp) is calculated by Pb−Pc. The steam saturation temperature Ts is obtained using Pb and/or Tb in an equation that approximate the saturated steam table. An example of such equation is:

$\begin{matrix} {{\log_{10}P} = {A + \frac{B}{T} + {\frac{Cx}{T}\left( {10^{{Dx}^{2}} - 1} \right)} + {E\left( 10^{{Fy}^{5/4}} \right)}}} & (1) \end{matrix}$

in which P=saturation pressure in international atmospheres

-   -   t=saturation temperature in degree of the international         temperature scale

T=t+273.16

x=T ² −K

y=374.11−t (374.11 taken as critical temperature),

and the parameters have the following values:

-   -   A=+5.4266514     -   B=−2005.1     -   C=+1.3869×10⁻⁴     -   D=+1.1965×10⁻¹¹     -   E=−0.0044     -   F=−0.0057148.¹ ¹Nathan S. Osborne & Cyril H. Meyers, A Formula         And Tables For The Pressure Of Saturated Water Vapor In The         Range 0 To 374 C, J. of Res. of the Nat'l Bureau of Standards,         Vol. 13 (1934), at 2.

Other equations for the saturated temperature (Ts) can also be used, as long as the approximated Ts is suited for practical use. Another commonly used equation is:

ln(T)=[a+bP _(r) +cP _(r) ² +dP _(r) ³ +eP _(r) ⁴]^(−0.4)   (2)

where P_(r) is the reduced pressure defined as P/P_(cr), wherein P_(cr) is the critical pressure, which is 22.064 MPa for steam. Parameters a-e are:

a b c d e 9.37817 × 4.98951 × 1.11049 × 3.34995 × 3.44102 × 10⁻³ 10⁻⁴ 10⁻⁵ 10⁻⁷ 10⁻⁸

The Pb and Tb are typically measured by a pressure sensor and a temperature sensor at the bottomhole, respectively. However, if a dual-functional pressure and temperature sensor is employed, only one sensor is needed. Such dual-functional pressure and temperature sensor is well known in the art and can be chosen by a skilled artisan for different downhole conditions.

As an additional feature, if the electric submersible pump (ESP) motor temperature exceeds its high alarm set point while the algorithm is in automatic control, the algorithm will not permit the motor to increase in speed. Normal control action from the sub cool, motor current, and submergence control loops to decrease motor speed are still permitted. When the alarm condition subsides, the control algorithms can once again increase speed.

The “Subcool Control Flow Chart” in FIG. 3 is provided for a graphical representation of the above. FIG. 3 shows each loop and control action regards to Current Value and Target Value.

The primary control loop is the subcool temperature loop (TIC) and it controls motor speed most of time, although the two secondary controllers will intervene under certain circumstances (e.g., when proposed change by the respective controller is the smallest positive change or largest negative change of the three proposed changes). The primary subcool temperature controller uses gap control with the PI algorithm.

A secondary PI controller (IIC) controls motor speed when its proposed change is smaller than those of the other two controllers (e.g., when motor current is too high). The IIC set point is set slightly below the high alarm set point and its algorithm slows the motor down if the motor current gets too high, prior to reaching the high alarm set point.

Another secondary PI controller (PDIC) controls motor speed when its proposed change is smaller than those of the other two controllers (e.g., when submergence pressure is too low). The PDIC set point is set slightly above the low alarm set point and its algorithm slows the motor down if the liquid level above the motor is too low, prior to reaching the low alarm set point.

Since the set points for these secondary controllers are close to their alarm set points and not near their normal operating values, they will only control in abnormal situations to protect the pump from reaching trip set point values and shutting down. Therefore, the subcool temperature remains the primary control mechanism.

The use of a gap control PI controller, that includes low select interventions for excess motor speed, excess motor temperature and too low submergence pressure provides a novel way of maintaining subcool and at the same time provides an automated subcool control system that is not easily oscillated in response to noise, but remains relatively stable in an SAGD environment, yet avoids excessive speeds and alarm tripping.

The present disclosure can be used in combination with, or before or behind, any other enhanced oil recovery method wherein subcool control is important, including steam drive, cyclic steam stimulation, VAPEX, SAGD, and the many SAGD variants such as JAGD, SW-SAGD, ES-SAGD, and combinations thereof.

The following are incorporated by reference herein in their entireties for all purposes.

SPE122014: SAGD Subcool Control with Smart Injection Wells (2012) by Gotawala.

WO2013135288 System and method for controlling the processing of oil sands. 

1. A method of automated subcool control in a steam-assisted gravity drive oil well, comprising: a) providing a producer well having one or more temperature sensors therein for measuring a temperature of a production fluid (Tb) and one or more pressure sensors for measuring pressure at bottomhole conditions (Pb), and one or more pressure sensors for measuring pressure at a casing head (Pc); b) providing a pump motor fluidly connected to said producer well for pumping a production fluid to the surface; c) calculating a submergence pressure Sp=Pb−Pc; d) calculating a steam saturation temperature (Ts) at Pb and Tb using an equation that approximates steam tables; e) providing a primary proportional integral (PI) controller for controlling subcool temperature (TIC) based on a gap control algorithm; f) providing a secondary proportional integral (PI) controller for controlling a current of said motor (IIC) when said pump motor's current approaches a high alarm set point; g) providing a secondary proportional integral (PI) controller for controlling a submergence pressure (PDIC) when said submergence pressure approaches a low alarm set point; h) wherein each said PI controller uses a low select algorithm to contribute a lowest value for adjusting a speed of said motor so as to approach a target subcool temperature (TΔ=Ts−Tb), maintain acceptable motor current, or acceptable submergence pressure.
 2. The method of claim 1, said pump motor further including a temperature sensor that measures the temperature of said pump motor, and further including an override function whereby said pump motor's speed cannot be increased when said pump motor's temperature reaches an alarm point.
 3. The method of claim 1, wherein said target subcool (TΔ) temperature is between 5-15° C./m with a gap allowance of ±1-5° C.
 4. The method of claim 1, wherein said target subcool (TΔ) temperature is 7-12° C./m with a gap allowance of 1-3° C.
 5. An improved method of subcool control in steam assisted gravity drive oil production, wherein steam is injected into a top horizontal well to mobilize heavy oil which gravity drains to a bottom production well and is then pumped to the surface using a pump and where a subcool is desirably kept at a target subcool, the improvement comprising automatically keeping a subcool at target subcool using a PI controller having an output that controls pump speed using a low select algorithm based primarily on gap control of subcool temperature.
 6. The method of claim 5, wherein a secondary PI control system intervenes with a low select algorithm when ii) a high alarm set point for motor current is reached or iii) a low alarm set point for submergence pressure is reached.
 7. The method of claim 5, further including an override function whereby said pump motor's speed cannot be increased when a temperature of said pump motor reaches a high alarm point.
 8. The method of claim 5, wherein said target subcool is 5-15° C./m and said gap is +/−1-5° C.
 9. An method of subcool control in steam assisted oil production, wherein a subcool is desirably kept at a target subcool using a PI controller having an output that controls pump speed using a primary low select and gap control algorithm based on subcool temperature, and secondary PI controller(s) intervene with a low select algorithm when ii) a high alarm set point for pump speed is approached or iii) a low alarm set point for submergence pressure is approached.
 10. The method of claim 9, further including an override function whereby said pump speed cannot be increased when a temperature of said pump speed reaches a high alarm point.
 11. A system for automated subcool control of a steam assisted oil recovery; said system including a gap control PI controller that adjusts a pump speed to maintain a target subcool, and includes a PI controller for low select intervention when said pump current approaches a high alarm value and includes a PI controller for a low select intervention when a submergence pressure approaches a low alarm value.
 12. The system of claim 11, said system further including a producer well having one or more temperature sensors therein for measuring a temperature of a production fluid (Tb) and one or more pressure sensors at bottomhole conditions (Pb) and one or more pressure sensors at a casing head (Pc).
 13. The system of claim 12, said system further including a temperature sensor on said motor and an override function whereby motor speed cannot be increased when a temperature of said motor reaches a high alarm point. 